Mounting device for crystalline rods

ABSTRACT

A device for mounting crystalline rods, such as semiconductor rods which are undergoing a floating zone melt treatment, comprised of a frame for supporting a rod and and having a plurality of axially extending open spaces in the peripheral boundary thereof, along with adjustable screws for mating with bores in the frame periphery for anchoring and centering a rod end within the frame.

United States Patent Sporrer Aug. 26, 1975 [54] MOUNTING DEVICE FORCRYSTALLINE 3,1 l3,84l 12/1963 Rcuschcl 23/301 SP RODS 3.189.415 6/1965Emcis 23/273 SP 3,191,924 6/1965 Haus 23/273 SP [75] Inventor: LudwigSporrer, Munich, Germany [73] Assignee: Siemens Aktiengesellschaft,Berlin, primary Examine, ROy Lake Germany Assistant ExaminerMark S.Hicks [22] Filed: 27, 1974 Attorney, Agent, or Firm-Hill, Gross,Simpson, Van

Santen, Steadman, Chiara & Simpson [21] Appl. No.: 446,160

[30] Foreign Application Priority Data ABSTRACT May 7, 1973 Germany2322969 A device for mounting Crystalline rods, Such as Semi I conductorrods which are undergoing a floating zone [52] 269/156 23/273 2 melttreatment, comprised of a frame for supporting a 269/287 269/321 279/83rod and and having a plurality of axially extending p spaces in theperipheral boundary thereof, along [58] held of Search 23/273 30] 279/83with adjustable screws for mating with bores in the 269/155 321 321 WEframe periphery for anchoring and centering a rod end within the frame.[56] References Cited UNITED STATES PATENTS 9/l96l Dorcndorf 23/301 SP 8Claims, 1 Drawing Figure MOUNTING DEVICE FOR CRYSTALLINE RODS BACKGROUNDOF THE INVENTION 1. Field of the Invention The invention relates tomounting devices and somewhat more particularly to mounting devices forsupporting ends of a crystalline rod while the rod is being processed bya floating zone melt process.

2. Background of the Invention In a typical floating zone melt process,a crystalline rod, such as composed of a semiconductor material, forexample, silicon, is mounted within a reaction chamber so that aninduction heating coil within the chamber encompasses an axial portionof the rod and upon energization of the coil, a zone of melt isgenerated on the rod. Relative movement between the coil and the rod iseffected so that the zone of melt floats along the length of the rodfrom one end to the other. This type of process is used to treat, forexample a semiconductor rod, in order to either concentrate impuritieswithin the rod at one end of the rod or to transform a polycrystallinesemiconductor rod into a monocrystalline rod. Generally, a seed or corecrystal is attached to a stock rod and the initial zone of melt isgenerated in the core crystal and then moved back and forth along thelength of the rod until a desired degree of treatment has been achieved.The rod (including core crystal) member is generally mounted verticallyat its opposite ends by a pair of mounting devices during such afloating zone melt process.

German Pat. No. 1,114,171 describes mounting devices for rod-shapedsemiconductor materials undergoing a floating zone melt process.Generally, these prior art mounting devices comprise a hollow framemember having three rotatable and resilient clamping means located intwo different planes, both of which are essentially perpendicular to thevertical axis of the frame and the axis of a rod mounted within theframe. The clamping means are actuatable by screws or studs mounted inthe frame member which have their ends in contact with the clampingmeans. Such devices have a relatively complicated construction and aredifficult to adjust to attain a proper centering of a rod mountedtherein. Further, the various components of such mounting devices,particularly the molybdenum studs, heat-up during a floating melt zoneprocess when the induction heating coil approaches a rod end since thecomponents extend into the field of the HF coil. The results in aloosening of the semiconductor rod since the mounting devices expand andallow the semiconductor rod mounted therein to fall out of the framemembers and become damaged and/or unsuited for further processing.

SUMMARY OF THE INVENTION The invention provides a rod mounting devicewhich substantially eliminates the aforesaid prior art drawbacks andcomprises a hollow frame member for mounting a rod end-and having atleast one open space extending in the axial direction of the framemember along with an adjustable screw matable with a bore within theframe for anchoring and centering a rod end within the frame.

It is a novel feature of the invention to provide a rod mounting devicecomprised of a hollow cylindrical frame member having threesomewhatM-shaped wall portions or U-shaped open spaces or recesses symmetricallyspaced about the periphery of the frame memher, with a threaded boreadjacent to each leg portion of the M-shaped wall portions and a screwfor mating with each bore and having a tip for holding and centering arod end mounted within the frame member.

It is another novel feature of the invention to provide a rod mountingdevice as described hereinabove, wherein the somewhat U-shaped openspaces have alternating solid wall areas between the leg portions of theopen areas and each solid area is of a different length than an adjacentsolid area. This arrangement prevents the high frequency field of aninduction heating coil from inducing any substantial heat or heatingcurrent into such a mounting device.

It is yet another novel feature of the invention to provide a rodmounting device as described hereinabove wherein alternate threadedbores are located in adjacent parallel planes perpendicular to a rodaxis. In a presently preferred exemplory embodiment, adjacent threadedbores are located at points in one of the two parallel planes so that aline joining the respective bore center points defines an angle of about60 with one of the parallel planes. This arrangement provides anextremely good centering and anchoring of a rod mounted within theframe.

Other and further objects of the invention will be apparent from thefollowing description and claims and are illustrated in the accompanyingdrawing which, by way of illustration, shows a preferred embodiment ofthe present invention and the principle thereof and what is nowconsidered to be the best mode contemplated for applying theseprinciples. Other. embodiments of the invention embodying the same orequivalent principles may be used as structural changes may be made asdesired by those skilled in the art without departing from the presentinvention and the purview of the appendant claims.

BRIEF DESCRIPTION OF DRAWINGS The single FIGURE is a perspectiveillustration of a rod mounting device constructed in accordance with theprinciples of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS U-shaped open spaces aresymmetrically spaced about the periphery of the frame member. In otherwords, the open spaces in the frame member are preferably spaced aboutapart about a rod axis within the frame member. The high frequency fieldof a coil can induce considerably less heating current into the framemember or mounting device through the open spaces, which extend in theaxial direction of the frame member. Further, the remaining solid areasof the frame between the open areas are resilient in respect to othersolid areas so that even if some slight heating of the frame memberoccurs during a zone melting process, the resiliency of wall portions ofthe frame member will maintain a semiconductor rod in its presetposition. These advantages are available in embodiments wherein only oneopen space or isolated wall portion is present in a frame member.

The preferred embodiment of the invention also include a plurality ofthreaded bores in the frame member which are spaced about the frameperiphery so as to be substantially symmetrically spaced about a rodaxis and mating screws or bolts which, in cooperation with the bores,anchor and center a rod end within the frame member. Preferably,alternate bores are dis posed in one of two parallel planes which extendperpendicularly to the vertical axis of the frame member, which is, ofcourse, parallel to a rod axis.

In certain and presently preferred embodiments of the invention, thethreaded bores are located adjacent the peripheral edges of the openspaces or recesses within the frame member and alternate bores aredisposed at a point in one of two parallel planes which extendperpendicularly to a rod axis so that a line joining the respectivecenter points of two adjacent bores defines an angle of about 60 withone of the parallel planes. This type of arrangement provides very goodcentering and anchoring of a semiconductor rod mounted within the framemember.

The screws or bolts utilized in the rod mounting devices of theinvention are preferably composed of steel and are provided with atungsten carbide (Widia metal) tips. Such screws provide a very goodattachment of a semiconductor rod since the screw tips tend to slightlywork into the surface of a rod and securely anchor the rod in place.Also, the preferred screws are provided with a milled screw head so thatbetter centering is achieved and centering tools or the like arerendered superfluous. Further, milled screw heads give an operator abetter feel of pressure during attachment of a semiconductor rod.

In certain preferred exemplory embodiments of the invention, the framemember and screws are composed ofa high grade steel, for example a steelhaving approximately a 19 percent chromium and approximately a 9 percentnickel content therein (V2A-steel). Such frame members and screws expanduniformly during a zone melt process and this type of steel does notgive off any detrimental oxidation impurities.

The rod mounting device of the invention allows one to mount and centervarious rod-shaped members having differnt diameters. In particular,very small diameter rods, for example core or seed crystal rods, arereadily mounted and centered with the mounting device of the invention.With frame members designated for mounting relatively thin rods, thewall thickness (or strength) of the frame member is matched to thediameter of the rod so as to achieve a good resilient effect. Thus,frame members adapted for small diameter rods have a reduced strengthwall in relation to a normal frame member. If necessary, nuts may beplaced onto the bores in order to attain better guidance of a milledscrew.

The rod mounting devices of the invention are espe cially useful in avacuum environment, such as sometimes present within a reaction chamberof a floating zone melt process, since lubricating means are notrequired.

Referring now to the exemplory embodiment of the invention illustrated,a hollow cylindrically shaped steel frame 1 is shown having threesomewhat U-shaped open spaces or recesses 3 milled into the peripheralwall of frame 1. The recesses 3 extend parallel to a rod axis 2 and aresymetrically spaced about axis 2. A plurality of bores 4 having internalthreads4a are spaced about the peripheral wall of frame 1. Intheembodimentshown, six bores 4 are provided adjacent each leg portion ofthe U-shaped openings or recesses 3. Alternate bores 3 are disposed inone of two parallel planes P and P which are perpendicular to the rodaxis 2 and are located at a point in one of the planes so that a line Ljoining their respective center points defines an angle a with one ofthe planes P or P of about 60. A steel screw 5 is provided for matingwith each of the bores 3 so that the screws tip 6, which is composed oftungsten carbide (Widia metal) extends into the interior of frame 1 andcontacts a semiconductor rod end (not shown) mounted within frame 1. Thescrew tip 6 works itself slightly into the surface of a semiconductorrod and provides a good attachment between the frame and a rod end. Thescrews 5 also has a milled head 7 which simplifies centering of a rodwithin the frame, since screw adjustment can easily be carried out byhand.

The drawings and specification presents a detailed disclosure of thepreferred embodiments mentioned and it will be appreciated that theinvention is not limited to the specific forms disclosed. Accordingly,modifications and variations may be effected without departing from thespirit and scope of the novel concepts of the invention.

I claim as my invention:

1. A device for mounting opposing ends of a semiconductor rod undergoinga floating zone melting treatment. with each rod end being supported byone such device, said device comprising a hollow cylindrically shapedframe member for encompassing a rod end, said frame member having aperipheral wall with three U-shaped recesses symmetrically spaced apartabout said wall, said peripheral wall having a plurality of threadedbores symmetrically spaced about said peripheral wall and screws matingwith said bores and securing the rod end within said frame.

2. A device as defined in claim 1 wherein alternate bores of saidplurality of bores are disposed in one of two parallel planes extendingperpendicularly to the axial direction of a rod mounted within saidframe.

3. A device as defined in claim 2 wherein said alternate bores arelocated at a point on said parallel plane so that a line joining thecenter points of said alternate bores defines an angle of about 60 withone of said parallel planes.

4. A device as defined in claim 1 wherein screws are provided withtungsten carbide tips.

5. A device as defined in claim 4 wherein said screws are provided withmilled heads.

6. A device as defined in claim 1 wherein said frame member and saidscrews are composed of a high-grade steel.

7. A device as defined in claim 6 wherein said highgrade steel includesabout 19 percent chromium and about 9 percent nickel.

8. A device for mounting an end of a semiconductor crystalline rodundergoing a floating zone melt treatment, comprising:

a hollow cylindrically shaped frame member for mounting an end of therod;

said frame member having a peripheral wall with three U-shaped recessestherein extending in the axial direction of the rod;

said peripheral wall having threaded bores adjacent spaced peripheraledges of said recesses; and screws for mating with said bores foranchoring and centering the rod end within said frame member.

1. A device for mounting ends of a semiconductor rod undergoing afloating zone melting treatment, with each rod end being supported byone such device, said device comprising a hollow cylindrically shapedframe member for encompassing a rod end, said frame member having aperipheral wall with three U-shaped recesses symmetrically spaced 120*apart about said wall.
 2. A device as defined in claim 1 whereinalternate bores of said plurality of bores are disposed in one of twoparallel planes extending perpendicularly to the axial direction of arod mounted within said frame.
 3. A device as defined in claim 2 whereinsaid alternate bores are located at a point on said parallel plane sothat a line joining the center points of said alternate bores defines anangle of about 60* with one of said parallel planes.
 4. A device asdefined in claim 1 wherein screws are provided with tungsten carbidetips.
 5. A device as defined in claim 4 wherein said screws are providedwith milled heads.
 6. A device as defined in claim 1 wherein said framemember and said screws are composed of a high-grade steel.
 7. A deviceas defined in claim 6 wherein said high-grade steel includes about 19percent chromium and about 9 percent nickel.
 8. A device for mounting anend of a semiconductor crystalline rod undergoing a floating zone melttreatment, comprising: a hollow cylindrically shaped frame member formounting an end of the rod; said frame member having a peripheral wallwith three U-shaped recesses therein extending in the axial direction ofthe rod; said peripheral wall having threaded bores adjacent spacedperipheral edges of said recesses; and screws for mating with said boresfor anchoring and centering the rod end within said frame member.